This invention relates to a method for processing a digital video tape recorder datastream. Specifically, the invention relates to inserting auxiliary data into the reproduced digital datastream.
High definition television (HDTV) signals typically are not compatible with current broadcast standards such as NTSC. A preferred signal coding standard suitable for use with the HDTV compatible signals is MPEG-2 (Motion Picture Experts Group, xe2x80x9cInformation Technologyxe2x80x94Coding of Moving Pictures and Associated Audio Information: Video,xe2x80x9d ISO/IEC 13818-2, May 15, 1996) as adopted by the Grand Alliance for use in the United States. This well-known standard provides formatting guidelines for coding and compressing video, audio and auxiliary data. Digital MPEG-2 compatible television signals may be terrestrially broadcasted, transmitted via a satellite link or sent via a cable system. Regardless of the transmission mode, an associated transport data stream will likely be completely occupied with data of one type or another.
When a signal reaches the consumer, current analog television/NVTR configurations allow the consumer to record one program on a video tape recorder (VTR) and watch another program simultaneously. It is also possible for a viewer to set the VTR to record a received program without the television receiver operating. In either situation, the viewer may play back the recorded program at a later time.
Video tape recorders typically insert data and messages into the playback video stream to indicate to the viewer the status of the VTR. On screen display (OSD) messages, for example, a PLAY or FF (fast forward) message, or an entire bit-mapped display, are displayed within the viewing image of the television screen with the video. The messages indicate that the viewer has activated the associated control on the remote control unit or on the front panel of the VTR and that the VTR is responding accordingly.
In an analog VTR system, one method of inserting an OSD message into the video signal at playback is by switching the OSD signal, for example, a DC voltage level, into the video signal. The switch occurs at the correct line and line position for the desired amount of time for display. When the OSD is removed, the video signal is uninterrupted by the switch.
For an MPEG-2 compatible incoming digital datastream containing the desired program to be recorded, the datastream is expected to be modulated and broadcasted to the consumer. The digital VTR (DVTR) receives the modulated signal, demodulates it, tunes to a particular channel and records the recovered datastream/channel on tape. For many reasons, it is not desirable to decode the MPEG-2 compatible encoded datastream either before recording or in playback. These reasons include the added cost of including decoding and formatting hardware in the DVTR, and potentially losing all but the primarily desired program if the datastream contains multiple programs. Because of the precise timing required to transmit an MPEG-2 compatible datastream, inserting auxiliary data into the capacity-filled datastream by overwriting data in selected packets would require decoding and encoding hardware, and recalculating presentation and display time stamps for the transport datastream. This is not desirable because of the associated cost and because of the loss of data which may be visible to the viewer. However, digital television receivers typically include the ability to mix OSD information into the video signal prior to display. Because of this, and because not all auxiliary data is OSD data, it is preferable to insert auxiliary data into a digital data stream without affecting the existing transport datastream rather than try to mix appropriate data into the video signal.
Therefore simple and efficient means to insert auxiliary data, such as OSD data, into the MPEG-2 compatible datastream is desirable. The invention presented herein provides such means.
A digital device receives digital program data including time stamps and inserts auxiliary information for transmission on a transmission channel. Prior to transmission, the digital device modulates the program data and the auxiliary information without altering the time stamps.